Means and method for secret signaling



H. D. ARNOLD.

MEANS AND METHOD FOR SECRET SIGNALING. APPLICATION FILED 050.30. 1916.

- 1,356,686. Patent/ad Oct. 26,1920.

/IH v01) for: Harv/a 0. Arno/d.

. nating current UNITED STATES PATENT OFFICE.

HAROLD D. ARNOLD, OF EAST ORANGE, NEW JER$EY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A OORPORA-.

TION OF NEW YORK.

MEANS AND METHOD FOR SECRET SIGNALING.

Specification of Letters Patent.

Patented Oct. 26, 1920.

Application filed December 80, 1916. Serial No. 189,945.

T 0 all whom it may concern: I

Be it known that I, HAROLD DE Fonns'r ARNOLD, a citizen of the United States, residing at East Orange, in the county of Essex and State of New Jersey, have inventedcertain new and useful Improvements in Means and Methods for Secret Signaling,

of which the following is a full, clear, conlight beams of such a character that the variations produced in the beams will be invisible to the naked eye, but can be readily detected by an observer provided with the necessary detecting apparatus as hereinafter described.

For the accomplishment of this purpose, this invention makes useof the well-established fact that the human eye unaided is insensitive to many of the qualities or characteristics of light beams. The particular characteristic employed in the following application of this invention is the inability ofthe eye to detect rapid oscillations of a high frequency. Thus, to the eye, the light is apparently the same from a source, such as a mercury lamp, an ordinary electric light bulb or an are or any other kind of a suitable lamp lighted by electricity, whether it is lighted by an alternating current frequency or by a. directicurrent, provided, however, that the effective lighting value is the same for the two currents.

For the better understanding of this invention, reference is made to the accompanying drawing, which illustrates this invention as adapted to a signaling system in which the signaling is accomplished by varying the frequency of the electrical current supply of a light source in accordance with the signals to be transmitted, and in detecting said variations in a stroboscopic manner.

In the transmitting station illustrated in the drawing, 3 is a source of light, shown here as an electric lamp, which may be supplied with direct currentfrom the source of current 4, or may be supplied with an alterfrom the generator 5. The lamp is preferably one in which the intensity of the light is sensitive to rapid changes in of a high current, such as that supplied by the alternatlng generator. 7 is a means by which the light may be alternately lighted by direct current and by alternating current. At the receiving station 9 is a stroboscopic means, shown here as a rotating perforated disk which serves to detect the above mentione changes in the current supply.

At the transmitting station the movable member 7 has an insulating block 10 which prevents a short circuit between the two adjustable contacts 13 and 14. With the contact 13 in the position illustrated, the resistance17 is in series with the battery 4 and is ofsuch a high value that actically no direct current flows through til: lamp. But with the contact 14 in the position illustrated, the resistance 19 is not included in the path of the alternating current from generator 5, so that little or no resistance is offered to the path of the alternating current through the lead wires 11 and 12 to the lamp 3, which path the current takes in preference to the high impedance path containing the battery 4. The frequency of this alternating current should be above that to which the human eye is sensitive probably above thirty cycles per second. h

At the receiving station the disk 9 is mounted on a shaft 21. On'this shaft is a pulley 22, which is connected to a source of power (not shown) by the belt 23 for rotating the disk at any desired speed. Near the outer edge of the disk, and spaced at regular intervals, are some rectangular slits or apertures, 24, through which the light from the transmitting station may be observed. If the frequency with which one aperture follows another is exactly twice that of the frequency of the generator 5, the eye, while gazing through said apertures, will be able to detect no change or flickering in the light received from the source 3 at the transmitting station as at every period the light is visible, the current through the source 3 will have the same value as the period before.

If, however, the speed of the disk is changed so that the apertures pass the line of sight at a frequency slightly greater or less than twice the frequency of the generator 5, a flickering will be observed, due to the fact that the light is being viewed through each aperture with the current in the filament l8 in a different portion of its cycle. This flickering is, therefore, an indication that the lamp is lighted by an alternating current.

If, now, the movable member 10 is adjusted so that the contacts 13 and 14 occupy the positions 13 and 14, respectively, resistance 19 is then included in the path of the alternating current from the generator, which resistance is of such a value that the alternating current willpractically be suppressed. Besistance 17, however, will be removed from the direct current circuit so that the current from the battery 4 will have a path of little resistance through contact 13', lead wires 11 and 12 to the lamp. Thus, with the adjustable contacts in the positions 13 and 14, the lighting of the lamp is accomplished by the direct current only. With such a source of current the light will consequently be steady so that no flickering at the receiving station will be observed through the stroboscope.

Hence, if by moving the sliding key 7, the current supplied to the lamp is varied from an alternating current to a direct current in accordance with the signals 'to be transmitted, an observer, looking through the apertures of the disk rotating at the proper speed, will be able to detect said signals, since the light will flicker when the lamp is lighted by an alternating current, but will remain steady when the lighting is done by a direct current. The signals are not visible, however, unless some suitable means, as the rotating disk illustrated, is used to detect them.

It is preferable that the relation between the values of resistances 17 and 19 should be such that for all positions of the sliding key between the points 13 and 14 and the points 13' and 14 the effective sum of the alternating current and the direct current will be constant so that the effective intensity of the light should remain constant as the key is moved from one position to another. Such a condition prevents the casual observer from detecting the signals and also increases the ease of the detection of the signals at the receiving station. 25 is a large condenser inserted in the alternating current generator circuit to prevent the flow of the direct current through said generator; but the condenser offers little or no impedance to the passage of the alternating current. 26 is a large choke coil in the direct current circuit which offers little or no resistance to the direct current, but prevents the alternating current from passing through the side circuit containing the battery 4.

It is apparent that any suitable means may be employed other than the one illustrated for changing the eflective lighting current from alternating to direct. It is also evident that any source of light deriving its energy from an electrical current, such as a mercury lamp or an electric are, for

example, may be substituted for the lamp shown. Various other modifications of the system may be made without departing in any wise from the spirit of this invention.

What is claimed is:

1. In a secret signaling system, a single source of light, means for varying an invisible characteristic of the visible light waves from said source in accordance with the signals to be transmitted while transmitting a substantially constant quantity of said visible light waves, and means for detecting said variations.

2. The method of secret signaling which consists in invisibly varying the frequency of a light beam in accordance with the signals to be transmitted and in detecting said signals stroboscopically. a

3. The method of secret signaling which consists in alternately transmitting a steady light and light of a given frequency in accordance with the signals to be transmitted while transmitting a substantially constant quantity of the normally visible characteristics of said light, and in rendering said signals visible.

4. In a secret signaling system, a source of light, two sources of current for said light source, one of which is an alternating current source, means for alternately lighting said light source by the two saidcurrent sources in accordance with the signals to be transmitted, and means for detecting said signals.

5. In a secret signaling system, an electric lamp and a source of current therefor, means for varying the current supplied to said lamp in accordance with the signals to be transmitted while transmitting a substantially constant quantity of the visible characteristic of the light from said lamp, and means for detecting said variations.

6. In a secret signalin system, an electric lamp and a source of current therefor, means for varying the current supplied to said lamp in accordance with the signals to be transmitted thereby changing the character of the light from said lamp, and a stroboscope whereby said changes may be detected.

7.- In a secret signaling system, a source of light, means for causing said source to emit steady light, a second means for causing said source to emit intermittent light having a frequency above that to which the naked eye is sensitive, means for alternately operating said source by said first means and by said second means in accordance with the signals to be transmitted and while transmitting a substantiall constant uantity of the visible characteristics of the ight from said source and means for detecting said signals.

8. In a secret signaling system, a source of light, a source of direct current for said light, a source of alternating current for said light, means for alternately impressing said currents on said light source thereby varying invisibly its light emission in a predetermmed order, and a receiver for detecting said variations.

9. In a secret signaling system, a source of light, means for causm said source to emit steady light, means or causing said source to emit intermittent light having a frequency above that to which the naked eye is sensitive, means for alternately operating said source by said first means and by. said second means in accordance with the signals to be transmitted, and a receiver for detecting said signals, said receiver consisting of a means for intermittently allowing said light to fall upon the observers eye.

10. In a secret signaling system, an electric lamp, a source of direct current for said lamp, a source of alternatin current for said lamp, means for alternate y impressing current from said sources on said lamp thereby varying invisibly its light emission in a predetermined order, and a receiver for detecting said variations, said receiver consisting of a rotating disk with apertures therein whereby said light may be viewed intermittently.

11. In a secret signaling system, an electric lamp, a source of direct current for said lamp, a source of alternating current for said lamp, means'for alternately impressing current from said sources on said lamp thereby varying invisibly its light emission in a predetermined order, a receiver for, detectin said variations, said receiver consisting 0 a diskwith perforations therein, and means for causing said perforations to follow each other with a frequency of the order of twice the frequency of said alternating current source.

12. The combination of a translating device, a plurality of means for supplying current thereto, and means for shifting from one of said mcansto the other while maintaining substantially constant the efiective value of the current supplied to said device during the shifting.

13. The combination of an electric lamp means for suppl ing alternating current and direct current t ereto, and means for gradualliyl shifting the current supply from one to t e other of said currents, Q

- 14. The combination of; an electric lamp, means forsuppl g-alternatingcurrent and direct current t ereto, and means for shifting the current supply from one of said currents to the other while maintaining substantially constant the intensity of the illumination of the light from the lamp.

15. The method WhlCh comprises supplying current from a source to atranslating device and substituting for said source a second source while supplying effectively the same amount of current to said device during the substitution of one of said sources for the other of said sources.

16. The method which comprises supplying current to a device at times from one source, supplying current to said device at times from another source and gradually shifting from one vof said sources to the other of said sources without disconnecting said device from said sources and while maintaining substantially constant "the amount of current supplied to said device during said shifting.

17. The method which comprises supply ing current to a translating device substantially entirely at times from one source sup-.

plying at other times current to said evice su stantially entirely from a second source and shiftin from one of said sources to the othero said sources while supplying 'efi'ectively the same amount of current to said device by gradually decreasing the amount of current'su plied by one 0 said sources and by gra ually increasing the amount of current supplied by the other of said sources until the current sugplied to said device is derived substantia y from one of said sources alone.

In witness whereof, I hereunto subscribe my name this 29th'day of December, A. D.

HAROLD n. ARNOLD. 

